Three people test positive to Legionnaire's disease in Sydney's south

Health authorities are trying to pinpoint the source of yet another outbreak of the deadly Legionnaire's disease in Sydney’s south.

Hospital officials have confirmed its cooling tower tested positive to the bacteria but whether that is the direct cause is still unknown.

Three people - two men aged 64 and 76, and an 85-year-old woman - have tested positive to the potentially fatal disease and had all spent time in Kogarah, including around St George Hospital.

They began to show symptoms between March 22 and 26.

One of the hospital's cooling towers returned a positive legionella result after testing on March 22 unrelated to the three cases and it has been decontaminated, but further tests are being carried out.

Other cooling towers in large buildings in the suburb are also being tested as authorities are uncertain whether the hospital's air-conditioning system is the source of the outbreak.